Identifying Critical Control Points in the Wild Oat (Avena fatua) Life Cycle and the Potential Effects of Harvest Weed-Seed Control

Abstract

Wild oat is a problematic weed species that requires new management techniques in the face of herbicide resistance; harvest weed-seed control (HWSC) may be an option. Wild oat demographic information was collected in long-term, rotational field studies in Lacombe, AB, Canada, in 2006 and 2007, and a periodic matrix model was parameterized using management extremes (no IPM, no herbicide to high IPM, and full herbicide). Population growth rates were calculated for each treatment and year. Prospective (elasticity) and retrospective (LTRE) analyses were conducted alongside a rearrangement of the model equation in which population growth rates were designated and the required proportion of newly shed seed survival that gives that growth rate was solved for. All populations had λ > 1 or increasing populations. Elasticity analyses indicated that λ was most-highly elastic to the overwinter seedbank (Esw = 1), followed by seedling survival, fecundity, and survival of newly shed seed (0.63 to 0.86 across treatments). The latter may be the most-accessible vital rate for management of herbicide resistant populations. LTRE exposed the stochasticity of wild oat population growth rates between years and their ability to take advantage of lapses in control. Decreasing the proportion of newly shed seeds (snew) that survives was the most-effective and available control strategy until reduced to 0.1 to 0.3 when the summer seedbank becomes more critical. When averaged across treatments, > 80% of newly shed seed must be eliminated to stop the population from growing, resulting in a stable population, but not a decline. Because of preharvest shattering, HWSC will likely not be effective enough alone to cause wild oat populations to decline. New management techniques for wild oat control that can be used in combination with HWSC and integrated weed management strategies are needed.

Assessing the effects of hybridization and precipitation on invasive weed demography using strength of selection on vital rates

“…In contrast, demographic estimates can account for both multi-generational survival and reproduction [37]. Certainly, in our study, although fecundity was the largest influence on population growth, differences in survival also played an important role in the differences in growth rate of these new populations and some risk assessment literature advocates their use [2, 79]. Here, we propose a second way they can be useful as a predictive, risk assessment tool.…”

Improving soil seed bank management

“…This machine, and other methods that only treat chaff materials, rely on the ability of the harvester to accurately separate weed seeds from straw and other heavy residues, so that dense weed seeds can avoid harvest weed seed controls by exiting the harvester along with heavy residues . Across methods, harvest weed seed control depletes the seed bank by limiting seed bank additions, but lasting effects on weed populations may only be observed if high proportions of seed are withheld from the soil seed bank …”

“…18 Across methods, harvest weed seed control depletes the seed bank by limiting seed bank additions, but lasting effects on weed populations may only be observed if high proportions of seed are withheld from the soil seed bank. 68 Just as selection pressure threatens any individual management practice, selection for phenotypes that escape harvest weed seed control will reduce longevity of the technique. Previously observed selection for early seed shattering 69 and increased seed density 70 could contribute to weed populations resistant to harvest weed seed control.…”

Narrow windrow burning canola (Brassica napus L.) residue for Sclerotinia sclerotiorum (Lib.) de Bary sclerotia destruction

“…In order to control multiple herbicide‐resistant weed biotypes, agroecologists have developed numerous techniques that intercept and kill weed seeds before they enter the soil [collectively termed harvest weed seed control (HWSC)] . Of all HWSC techniques, narrow windrow burning is the most widely adopted in Australia, requiring growers to capture weed seeds mechanically at harvest and concentrate them into a narrow windrow, 0.7–1 m wide, at the rear of the harvester with the chaff fraction . In the following autumn, these narrow windrows are burnt, achieving sufficient temperatures for sufficient length of time to kill the intercepted weed seeds .…”

“…13 Of all HWSC techniques, narrow windrow burning is the most widely adopted in Australia, requiring growers to capture weed seeds mechanically at harvest and concentrate them into a narrow windrow, 0.7-1 m wide, at the rear of the harvester with the chaff fraction. [13][14][15][16] In the following autumn, these narrow windrows are burnt, achieving sufficient temperatures for sufficient length of time to kill the intercepted weed seeds. 13,17 Like weed seeds, S. sclerotiorum sclerotia are commonly found as contaminants in harvested canola seed, indicating that sclerotia located above a harvest cutting height are intercepted during grain harvest.…”